Group Dependabot updates

[samdark]

Replicates the Dependabot grouping configuration from yiisoft/package-template so GitHub Actions updates are grouped into a single PR and Composer dependency updates are grouped into a single PR.

[Copilot]

Pull request overview

Note

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Updates Dependabot configuration to reduce PR noise by enabling grouping of updates (GitHub Actions into one PR, Composer dependencies into one PR), mirroring the setup used in yiisoft/package-template.

Changes:

• Enable grouped Dependabot updates for the github-actions ecosystem (weekly cadence).
• Enable grouped Dependabot updates for the composer ecosystem (daily cadence).
• Add a 7-day cooldown configuration to reduce update frequency.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (cd52954) to head (ce4fbed).

Additional details and impacted files

@@             Coverage Diff             @@
##              master      #232   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity        48        48           
===========================================
  Files              4         4           
  Lines            104       104           
===========================================
  Hits             104       104           

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